As the life-saving benefits of hazardous condition detectors are recognized, their usage continues to expand. Such hazardous condition detectors include smoke detectors, heat detectors, carbon monoxide detectors, flammable vapor detectors, combination units, etc. Indeed, the installation of such detectors is mandated in many states by building code for all new construction of single and multi-family dwellings, office buildings, schools, etc. Further, many areas also require that such detectors be installed in existing homes before they may be sold.
Because many such structures include multiple floors, rooms, or areas on or in which a remotely located hazardous condition detector may not be heard, it is recommended that multiple hazardous condition detectors be located throughout the structure or dwelling to increase the likelihood of early detection of a hazardous condition. Such early detection is a direct factor in the survivability of the occupants within the dwelling or structure.
In a typical single family dwelling having a basement and two stories, at least one hazardous condition detector should be placed on each floor of the dwelling. That is, at least one detector should be placed in the basement, on the first floor, and on the second floor. In this way, a hazardous condition that originates in the basement may be detected sooner than if the only hazardous detector were located on the second floor. Indeed, even in single floor plan dwellings or structures, it is recommended to include multiple detectors at various locations. For example, a hazardous condition detector may be located in the utility room housing the furnace, water heater, etc., one in the kitchen and one in each of the bedrooms or in the hallway by the bedrooms. Regardless of the configuration, however, the use of multiple hazardous condition detectors provides the advantage of detecting the hazardous condition early to allow the occupants as much time as possible to avoid danger.
While the use of multiple hazardous condition detectors at different locations throughout a dwelling or structure increases the likelihood of detecting a hazardous condition early, the layout of the dwelling or structure may well prevent an occupant from hearing the alarm of the hazardous condition detector located in proximity to the hazardous condition when it sounds. For example, if the hazardous condition detector in the basement of a two-story single family dwelling were to detect a hazardous condition and sound its alarm, the occupants who may be asleep on the second story may not be able to hear the alarm sounding in the basement. Indeed, many dwellings are constructed with insulation between the stories for the very purpose of stopping the transmission of noise therebetween. However, such sound insulation may well detract from the advantage of installing multiple hazardous condition detectors throughout the dwelling. If the hazardous condition continues to expand, the other detectors in the dwelling or structure will eventually detect this hazardous condition and hopefully alert the occupant of the existence of such a condition in time for the occupant to escape the danger.
To overcome this problem, the hazardous condition detectors may be interconnected or networked together utilizing a wired connection. In such installations the hazardous condition detectors communicate among themselves via a single wire in a three wire interconnect, the other two wires providing electric power to the units. In such an installation the detecting hazardous condition detector sounds its alarm and transmits a hazardous condition detected signal to the other interconnected hazardous condition detectors. These detectors then sound their alarm to notify the occupant of the detected hazardous condition within the dwelling.
While the sounding of the alarm of each of the interconnected hazardous condition detectors will increase the likelihood that the occupants will be advised of the hazardous condition, it is imperative that the wrong alarm is not sounded. That is, it is common for many dwellings or structures to include multiples types of hazardous condition detectors, each having a distinctive alarm pattern to alert the user to the different types of detected hazardous conditions. For example, a typical single family dwelling may include both smoke and carbon monoxide detectors. In such an installation, the detection of smoke must result in only smoke alarms being sounded throughout the dwelling. That is, no carbon monoxide alarm signal should be sounded by a carbon monoxide detector because smoke is detected by one of the other hazardous condition detectors. The converse is also true.
If each different type of detector were to sound its alarm, the occupant would most likely become confused, and may well take the wrong action. For example, if both smoke and CO alarms are sounding when a fire is detected, the occupant may well believe that CO has been sensed and take time to open windows to let in fresh air instead of fleeing the structure. In view of this requirement, only the hazardous condition detectors that are capable of sounding the alarm corresponding to the detected hazardous condition should sound such an alarm. The other hazardous condition detectors that are not capable of sounding an alarm that corresponds to the detected hazardous condition must remain silent to avoid confusing the occupants as to the detected hazard.
As indicated above, the typical hazardous detector system interconnect utilizes a three wire system. Two of the wires are used to provide AC power to the detectors, while the third is used to transmit the remote alarm signal. This interconnect system was developed originally for the interconnection of smoke detectors. For simplicity, the interconnected smoke detectors simply apply a DC signal on the interconnect of at least about 3.0 Vdc. When the other smoke detectors sense this DC level on the interconnect, they sound their alarm. To prevent high frequency transients and 50 and 60 Hz modulation signals (associated with input AC power) from triggering the local alarm, the smoke detectors typically include an interconnect filter such as illustrated in FIG. 1.
Briefly described, the interconnect filter of FIG. 1 includes a resistor and capacitor that serve as a low-pass filter, i.e., to generally allow only low frequency signals to reach the smoke alarm sensing circuit portion from the interconnect line. A constant (DC) voltage signal present on the interconnect line charges the capacitor through the resistor. When the voltage at the capacitor reaches the predetermined threshold value (for example, at least about 3.0 volts at the interconnect port) an alarm indicator is triggered. The Zener diode clamps any inappropriate voltage spikes across the capacitor to a sufficiently low level to help prevent damage to alarm circuit portion.
With the relatively recent addition of carbon monoxide (CO) detectors in the home, a system was needed to allow such detectors also to be interconnected while ensuring that the smoke detectors would not erroneously sound their alarm when CO was sensed. While a separate interconnect could have been used only for the CO detectors, such an approach greatly increases the cost and complexity of the interconnect wiring needed in the dwelling. Further, the recent advent of combination detectors, providing both CO and smoke detection in a single package, further makes such an approach unworkable.
One system of providing communication between hazardous condition detectors that allows communication of both smoke and CO alarm signals on the single signal wire of the interconnect, and that ensures that erroneous alarms are not triggered is provided in U.S. Pat. No. 6,611,204, entitled “Hazard Alarm, System, and Communication Therefore”, the teachings and disclosure of which are hereby incorporated in their entireties by reference thereto. This system provides a digital signal on the interconnect wiring signal line when a carbon monoxide hazard has been detected. Since the typical smoke detector filters high frequency signals, the digital signal indicative of CO is not seen by such smoke detectors as a command to sound their alarm. Similarly, the presence of a DC voltage signal on the interconnect signal wire is not read by the CO detectors as a command to sound their alarm.
While such a system provides a significant advancement in the art, it is still possible for both smoke and CO alarms to sound at the same time. This condition may result when both smoke and CO are detected by the detectors, a condition that may be present during a real fire. Since the sounding of both types of alarms may be confusing to the occupants, potentially causing them to take the wrong or inappropriate action, this is to be avoided.
Further, once a hazardous condition has been detected and all interconnected alarms are sounded, the occupant may be unaware of the actual location of the hazardous condition that originated the alarming. Without such information, the occupants may well place themselves in danger by going toward the hazard or by taking an escape route that would increase their risk of injury. Unfortunately, with all of the interconnected hazardous condition detectors sounding their alarm, the occupants may not be able to make an informed decision of which escape route to take.
In view of the above, there exists the need in the art for a system and method of communication between hazardous condition detectors that distinguish different detected hazardous conditions and that prioritizes the different hazardous condition alarms while communicating on the existing interconnect system. This is needed so that the occupants may be quickly and properly advised of the most serious threat to their safety and well being. There also exists a need in the art for a system and method of communication between hazardous condition detectors that allows an occupant to hush all of the interconnected detectors' alarms except for the detecting detector so that the location of the hazardous condition may more easily and safely be determined.